The object of a device according to the present invention is to keep the flow constant by combining a pressure difference valve with an integrated check device. The check device can also be varied by choosing in a stepless manner a more or less open check device in order to in this way in the separate case let the desired flow reach a chosen pressure difference level.
The already known devices, designed to meet these objects, and in these cases primarily pressure difference regulators or flow regulation valves, are impaired by various drawbacks.
A device, based on a pressure difference regulator, in principle can limit the flow to a level, which depends on the chosen pressure difference across the valve and the size of the valve, i.e. the flow, which it is chosen to be able to limit the pressure for. The limitation is caused by the fact, that, when a smaller flow is needed, a flow, which is smaller than the predicted one, to the valve, which is related to a definite pressure difference, must be added a valve, which eliminates this too large flow. In this case this separate valve can be allowed to operate with a pressure level, which may cause noise, since the chosen pressure difference valve cannot check this smaller flow and thus not limit the pressure for this smaller flow. Consequently, two different valves must be combined. One pressure difference valve and one flow regulating valve in order to obtain the desirable regulation functioning is of course an expensive solution.
A device, based on a flow regulation valve, can of course limit the flow, but such a system must include valves, which also limit the available pressure difference across the flow limitation valve. This means, that regardless of what system of the two mentioned above, which is chosen, the set-up must comprise at least two separate units, one which limits the pressure difference level and one which regulates the flow.
In small set-ups, e.g. in small houses, the pressure levels are normally not so high, that the above-mentioned combination of difference- and flow limitation functions are required. In these set-ups radiator valves are used, which can be designed to allow the opening between the cone and the seat of the valve to vary in various ways in order to be able to regulate the flow in a better way.
Examples of solutions for small set-ups are described in SE 8600679-8 and in DE 27 56 118.
For large set-ups, i.e. often set-ups with high pressure differences, there are constructions, which are based on a limitation of the flow in steps, which arrangement is described in e.g. EP 0 591 873 A 1, and as an alternative a use of a pressure difference valve according to e.g. U.S. Pat. No. 6,196,259 B1.
In all these existing solutions the total cost is high, in case a satisfactory functioning in a set-up is to be achieved, partly because several units are required and partly because the existing pressure difference valves often are complicated constructions. Since at least one pressure reducing function and one flow limiting function are required, in most set-ups, the final cost for the client will be high. Two components must be installed and these often require some type of maintenance or control, which means elevated costs.